This invention relates to a colored, anodized aluminum-base article.
More specifically, the present invention is concerned with a colored, anodized aluminum-base article having two kinds of anodized aluminum oxide films overlaid on an aluminum-base substrate. The present invention is also directed to a method of preparing such an article.
It is well known in the art that aluminum or an aluminum alloy can be improved in its corrosion and weather-resistance by forming an anodized aluminum oxide film on the surface thereof. There are known several different kinds of anodic aluminum oxide film, such as so called ordinary and hard anodic oxide films. The ordinary anodic oxide film is produced by anodizing aluminum or its alloy in an electrolyte bath, such as sulfuric acid bath, at a temperature of 20.degree.-40.degree. C. generally under direct current conditions. This film is clear and porous and, therefore, is suited for being colored. However, the corrosion-resistance of the film is not sufficiently high because of the high porosity and a large pore diameter thereof. On the other hand, the hard anodic oxide film is prepared by the anodization of aluminum or its alloy at a temperature of not higher than 10.degree. C. The hard film is less porous and has a greater thickness than the ordinary anodic oxide film and, hence, exhibits a high corrosion-resistance. However, the low porosity and the small pore diameter of the pores of the film make it difficult to color the hard film.